We plan five areas of research centered on the elucidation of the structure and function of bacteriorhodopsin (bR), rhodopsin (Rho), and halorhodopsin (hR) with high resolution, solid state NMR. (1) We plan to investigate the opsin shift in Rho and other retinal proteins by recording chemical shift anisotropies of 13C labeled retinal in Rho, in a series of 11-cis and 9-cis PSB's, and in "colored mutants." (2) We plan three parallel studies of the photointermediates of bR -- bR568, L550, M412, and N520. (2.1) Structure of the retinal, the Lys216 sidechain, and the Schiff base N: We plan to determine the orientation and structure of the retinal and the Schiff base linkage with angular dependent studies of partially oriented samples of bR (on glass plates) labeled as -CD3 at C-18, 19, and 20 and 15N at the SB linkage in the M, L and N intermediates trapped at low temperatures The L and M experiments will be performed at equal to or less than 150 K where it is possible to employ dynamic nuclear polarization (DNP) to enhance the NMR signals. This involves doping the H2O in these samples with paramagnet centers and irradiation with high frequency microwaves. In other experiments, the structure of the Lys sidechain in these intermediates will be determined with 13c-13c and 13C- 15N MAS recoupling experiments designed to detect the presence of gauche bonds. With 12-13C and epsilon15N-Lys labeled bR we plan to resolve if the L state is 13-cis, 14-trans or 13,14-dicis. (2.2) Structure of the Retinal Binding Pocket: The SB linkage and the retinal are surrounded by a number of amino residues -- D85, D212, R82, Y185, M118, W182, etc. -- whose positions in bRDA are known with varying precision from the electron diffraction model of Henderson. We plan to study the changes in the position of these residues, and thus the structure of the retinal binding pocket, which occur in bR568, L, M, and N intermediates with 2D MAS homo and heteronuclear recoupling techniques. (2.3) H+ pumping pathway and H2O in bR: A third area of interest is the H+ pathway during the pumping cycle and the position and disposition of H2O associated with bR. These aspects of bR will be investigated with multidimensional 1H MAS experiments at higher fields, where we will have improved resolution. Further, we plan to explore new approaches to increasing the resolution in H+ exchange spectra in order to elucidate the H+ conduction pathway. (3) The hR experiments will be focussed on studying the opsin shift mechanism in this protein, the state of two His residues and the binding of anions to the protein.